The subject matter disclosed herein generally relates to controlling emissions in an internal combustion engine and more particularly to methods and systems controlling emissions using active control of the temperature at the inlet of an ammonia slip catalyst assembly (ASC).
Environmental regulations require the use of catalysts to treat engine exhaust in order to reduce air pollution. A catalytic converter uses two types of catalysts, a reduction catalyst and an oxidation catalyst. The catalytic converter consists of a ceramic structure coated with a metal catalyst incorporated within a housing. The catalytic converter provides a structure that exposes the maximum surface area of catalyst to the exhaust stream.
A three-way catalyst assembly (TWC) is employed on stationary rich-burn engines to reduce the emissions of nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO). Because these engines operate under rich conditions, a significant portion of the engine out NOx is converted to ammonia (NH3) over the TWC and is consequently emitted as a secondary emission. A typical rich-burn engine equipped with a TWC catalyst may emit around 400 ppm NH3 at richer than stoichiometric conditions.
NH3 emissions may be reduced with the use of an ASC. An ASC converts NH3 to N2. However, if the temperature at the ASC exceeds the catalyst operating window (400-510° C.), NH3 may be oxidized to NOx which results in the system exceeding NOx regulations.